When asbestos-cement roofing tiles are manufactured by a dry method, a dry mixture of asbestos and cement is placed on a belt conveyor in the form of a layer having a specified thickness, and the layer is thereafter subjected to the step of wetting with water, coloring step, compressing step, cutting step, etc., to obtain uncured or green panels having the shape of the roofing tiles.
At the terminal end of the belt conveyor, the green panels are transferred from the belt conveyor to a table as stacked in the form of a block of specified number of panels. The block is then spontaneously cured, sent into an autoclave for curing and dried to obtain asbestos-cement roofing tiles. Although the cured tiles are tough, the green panels prior to the spontaneous curing are very soft and extremely susceptible to impact and bending. Conventionally, the green panels are transferred from the belt conveyor onto the table directly by the hands of the worker but, when handled manually, the green panels are very prone to damage.
In order to overcome this problem, we have already provided a stacking device including a vertically movable inclined table and disposed at the terminal end of the belt conveyor. The table is adapted to receive the panels from the conveyor in such manner that every time a panel is transferred onto the table, the table is lowered by an amount corresponding to the thickness of the panel, permitting the next panel to be slidingly transferred from the conveyor onto the panel already retained on the table, whereby the panels are stacked on the table. Although the panels can be stacked accurately with use of this device, the operation still involves the following drawbacks.
Since the green panel has a great coefficient of friction, the inclined table must have a large angle of inclination so as to enable the green panel to slidingly fall onto the table from the belt conveyor, with the result that the downwardly sliding panel is liable to damage on striking a stopper at the table end. Further when sliding on the surface of the panels stacked on the table, the panel tends to deface the underlying green panel or to roughen the surface thereof, pilling the asbestos fibers incorporated in the panel.
Thus, it has been difficult to transfer soft panels, such as green roofing tiles, from the belt conveyor free of damage and deformation.